Method of plasma beam bombardment of aligning films for liquid crystals

ABSTRACT

Methods for treating aligning substrates produces uniform alignment of liquid crystals in at least two modes. The method is based on the treatment of liquid crystal aligning substrates with a collimated or partially collimated plasma beam. In one embodiment, the method comprises a step of bombarding an aligning substrate with at least one plasma beam from a plasma beam source at a designated incident angle to align the atomic/molecular structure or the surface profile of the aligning substrate in at least one aligned direction.

FIELD OF INVENTION

The present invention relates to methods of uniform alignment of liquidcrystals (LCs) of both thermotropic (solvent-independent) and lyotropic(solvent-based) type. More particularly, this method is based on thetreatment of LC aligning substrates with a collimated or partiallycollimated plasma beam. In one embodiment, the method comprises the stepof bombarding an aligning substrate with at least one plasma beam from aplasma beam source such as a closed drift thruster, preferably an anodelayer thruster, at a designated incident angle to align theatomic/molecular structure and/or the surface profile of the aligningsubstrate in at least one aligned direction. The method can be used toproduce at least two modes of uniform alignment, one mode with the “easyaxis” in the incident plane of plasma beam, and a second mode with the“easy axis” perpendicular to the plane of incidence.

BACKGROUND OF THE INVENTION

A uniform surface alignment of liquid crystals (LCs) is an importantproblem in practical applications of liquid crystal cells. In the caseof uniform alignment, the direction of the average orientation of LCmolecules on the substrate can be described by two angles—zenithal angleθ (the angle between the substrate and the direction of LC averageorientation, also called the pretilt angle of the LC, and the azimuthangle φ (the angle in the plane of the substrate, measured between thedirector and some axis). In absence of external torques, the two angleshave well-defined equilibrium values or range of values that aredetermined by the specifics of molecular interactions at the liquidcrystal-substrate interface. These equilibrium values determine one,two, or more “easy axis” or “easy axes” directions. The angle θ can beused to classify the types of uniform alignment of LC. Three cases canbe cited:

-   -   1) homeotropic (also known as perpendicular or normal) alignment        characterized by preferential orientation of LC molecules in a        direction normal to the film. In this case LC pretilt angle θ is        equal to 90°    -   2) planar alignment characterized by uniaxial ordering of LC        molecules in plane of the aligning substrate (θ equals 0).    -   3) tilted alignment with the orientation axis obliquely oriented        with respect to the aligning substrate. For this type of        alignment 0°<θ<90°.

The first type of alignment implies that the azimuth angle φ is notspecified, whereas 2) and 3) types are characterized by a well-definedvalue of the azimuth angle φ, when the medium adjacent to the LC isanisotropic. The azimuth direction might be degenerate, i.e., φ is notspecified, when the adjacent medium is isotropic in the film plane.

As a rule, homeotropic alignment of LC can be relatively easy obtainedfor both thermotropic and lyotropic LCs. Thermotropic materials acquiretheir mesomorphic (orientationally ordered) state when the material iswithin a certain temperature range. Lyotropic materials becomemesomorphic when dissolved in some solvent (such as water), within anappropriate concentration range. The most common method of homeotropicalignment is a treatment of the aligning substrates with surfactantmaterials. In contrast, great skill is required to obtain planar ortilted alignment with desirable alignment parameters such as the azimuthangle φ, strength of anchoring, etc. The problem is challenging for boththermotropic and lyotropic LCs. The most common technique for such acontrolled alignment is a unidirectional rubbing of special aligningfilms (e.g., polymer films) deposited at the bounding substrates.However, this method often hinders the further improvement of thedevices based on LC cells because of several principal drawbacks. Therubbing process causes surface deterioration as well as generation ofelectrostatic charges and dust on the aligning surfaces. Besides, it isnot convenient for the fabrication of LC cells having some specialstructure, for example, multidomain cells. The reason is that therubbing method implies mechanical contact with aligning substrates.

To avoid the problem, a number of non-contact LC alignment methods hasbeen suggested. Among them the photoalignment method is the mostpromising and intensively studied. Using this method, substrates arecovered by photosensitive materials and subsequently irradiated withpolarized UV or visible light. The photoalignment method allowscontrolling of LC anchoring and easy axis direction in both azimuthaland polar planes. This makes possible patterned alignment used toenhance viewing angles in nematic LCD. However, the photoaligningtechnique is usually accompanied with a low anchoring strength andrelatively poor photo and thermal stability. Besides, LC alignment onthe photoirradiated substrates is characterized by the pronounced imagesticking effect which is a residual image when the controlling voltageis changed.

From the first sight, the main problem of photoalignment is a problem ofuseful materials. However, following literature data, practically allphotoaligning materials developed up to this date more or less sufferfrom the drawbacks mentioned above. This gives the reasons to concludethat shortcomings of photoalignment are mainly associated with treatmentprocedure. As we believe, the action of UV/Vis light modifies thealigning surface only “softly” and so it is not capable to create strongboundary conditions for LC layers.

To overcome shortcomings of the conventional photoalignment method, M.Hazegava suggested to use deep UV irradiation. He showed that 257 mnirradiation causes LC alignment effect on the polymers, which arenon-sensitive to conventional UV/Vis light. One more radical solution issuggested by Chaudhari et al. It consists in oblique irradiation of thealigning polymer substrates with a collimated or partially collimatedion beam. This method provides excellent LC alignment on both organicand non-organic substrates. Later on, several modifications of the iontreatment method have been suggested. In the aligning substrate isbombarded with ions at normal incidence in the presence of an electricfield, which is applied in the area close to the substrate. In this casethe applied field is sufficient to redirect ions obliquely to thesubstrate. The other modification is proposed in where ion beamirradiation is used in combination with rubbing to produce two-domainpatterning of the aligning substrate.

The advantages of deep UV irradiation and ion irradiation can becombined by the treatment of the aligning substrates with various kindsof plasma. The processing of LC substrates with the glow discharge wasearlier applied for surface etching, grafting of the aligning surfaceswith various atoms, as well as plasma polymerization. In comparison toprior art plasma methods that include deposition of various films [J. C.Dubois, M. Gazard, and A. Zann, 1974, Appl. Phys. Letters, 24 (7),29738-40; R. Watanabe, T. Nakano, T. Satoh, H. Hatoh, and Y. Ohki, 1987,Jpn. J. Appl. Phys., 26(3), 373, and A. I. Vangonen, and E. A. Konshina.1997, Mol. Cryst. Liq. Cryst., 304, 507] and post-deposition treatments,mainly by bombardment with reactive ions [N. Shahidzadeh, A. Merdas, andW. Urbach, 1998, Langmuir, 14, 6594, 41-43; J. G. Fonseca, P. Charue,and Y. Galerne, 1999, Mol. Cryst. Liq. Cryst., 329, 597; and S. P.Kurchatkin, N. A. Muravyeva, A. L. Mamaev, V. P. Sevostyanov, and E. I.Smirnova, Patent of Russia No 2,055,384.], the technique of the presentinvention has a number of advantages. All the previously known methodslisted above are reportedly capable of producing various values ofzenithal anchoring coefficient and pretilt angle but not a uniformplanar alignment; mostly because the substrates are placed in the gasdischarge area where the plasma treatment is practically isotropic.Sprokel et al. [G. J. Sprokel and R. M. Gibson, 1977, J. Electrochem.Soc., 124(4), 559] proposed a directed plasma flux and anisotropictreatment, which resulted in a uniform planar alignment. This wasachieved by the use of a modified r.f. plasma etcher in which reactiveplasma was extracted and carried onto substrates by the gas stream. Thetechnique of alignment set forth in this invention is extremelyversatile, as it allows one to align both the thermotropic LCs such asthe ones used in LC displays and lyotropic LCs, such as lyotropicchromonic LCs used in optical elements and biological sensors, see C.Woolverton et al., U.S. Pat. No. 6,171,802; O. D. Lavrentovich and T.Ishikawa, U.S. Pat. No. 6,411,354 and O. D. Lavrentovich and T.Ishikawa, U.S. Pat. No. 6,570,632. Moreover, all these liquidcrystalline materials can be aligned at a broad variety of substrates,both inorganic and organic.

SUMMARY OF THE INVENTION

The present invention provides aligning substrates for uniform alignmentof liquid crystals (planar, tilted and homeotropic) comprising organicand non-organic films treated with a collimated or partially collimatedplasma beam, from a plasma source which is preferably an anode layerthruster.

The present invention also provides a method of making an aligningsubstrate comprising: providing an aligning substrate or film andirradiating or bombarding it with a collimated or partially collimatedplasma beam.

The plasma beam irradiation method of the present invention results inat least two modes or types of uniform alignment when the irradiation isperformed at tilted incident angles: (1) an easy axis that is confinedto the incident plane formed by the direction of the beam and the normalto the treated substrate; (2) an easy axis that is perpendicular to theplane of incidence. By increasing the irradiation dose one can changethe alignment direction from the type (1) towards the type (2). In thefirst type of alignment, the value of the pretilt angle can becontrolled, wherein pretilt angle θ is 0° to less than or equal to 10°for LC with positive dielectric anisotropy (Δ∈>0) and 0° to less than orequal to about 40° for LC with negative dielectric anisotropy (Δ∈<0),with irradiation parameters (irradiation angle, ion current density, ionenergy, etc.). The second type of alignment is characterized by a zeropretilt. Two-mode alignment feature can also be used to generatealignment with desirable parameters as well as to pattern LC cell(s).

The present invention also provides a class of plasma sources which canbe used to generate uniform LC alignment. As an example of suitableplasma source, the anode layer thruster is disclosed. In our experimentsof the present invention, plasma is extracted and acceleratedelectrostatically to relatively low energies that treat only a thinlayer of the substrate. Thus the anode layer thruster plasma sourceallows one to combine the advantageous anisotropic treatment withcollimated or partially collimated plasma fluxes and the optimizedenergies of ions. The anode layer thruster plasma source can be scaledup to treat substrates of large size (meters). Reliability, simplicityof construction, high thrust efficiency and easiness of treatment ofsubstrates make this source attractive for technological applications.

One of the main advantages of the described procedure is that it yieldsseveral regimes of LC alignment, as specified below for the typicalthermotropic LC materials such as nematic LC K15 pentylcyanobiphenyl(5CB):

-   -   1) First mode which is usually characterized by planar alignment        with a relatively weak azimuthal anchoring coefficient        W_(a)=10⁻⁶−10⁻⁵ J/m² or higher and relatively high pretilt angle        θ=(about 5°-about 10°) for LC with Δ∈>0 and θ=(about 5° to about        40°) for LC with (Δ∈<0);    -   2) Second mode which is characterized by planar alignment with        relatively strong anchoring (W_(a)>10⁻⁴ J/m²) and zero pretilt        angle; and    -   3) Subsequent treatment using the combinations of the basic two        modes above which is characterized by, planar alignment with        strong anchoring (W_(a)>10⁻⁴ J/m²) and moderate pretilt angle        θ=(0°-about 5°).        Each of these regimes is attractive for modern LCD technologies        in which the thermotropic LCs are used. The first alignment        regime may be useful for LCD based on the easy axis gliding. The        second regime is promising for bistable nematic displays.        Finally, the third regime and, possibly, the first regime for        some aligning materials may replace standard rubbing procedure        widely used in modern LCD technology. The regimes above are also        of practical importance in aligning lyotropic LC such as        lyotropic chromonic liquid crystals (LCLCs) that can be used in        optical and sensing applications, see C. Woolverton et al., U.S.        Pat. No. 6,171,802; O. D. Lavrentovich and T. Ishikawa, U.S.        Pat. No. 6,411,354 and O. D. Lavrentovich and T. Ishikawa, U.S.        Pat. No. 6,570,632 herein incorporated by reference.

The two-mode alignment opens new opportunities for the patterning of LCalignment. For instance, the two-domain azimuthal patterning can berealized by only one masking step without any rotation of the substrate.Evidently, all patterning procedures described for other etchingalignment methods are also feasible in the present invention. Moreover,for sample patterning, the plasma alignment method may be combined withother methods of LC alignment.

Finally, it is worth mentioning that the proposed aligning procedure iscompatible with other vacuum processes employed in LCD industry,including but not limited to, ITO deposition, TFT coating, vacuumfilling of LCD, etc. An entirely vacuum technological line of LCDproduction is envisioned which can strongly reduce the well-knownproblems related to dust, humidity, air ions etc.

In one embodiment, a method for generating an alignment direction on analigning substrate for liquid crystal cells is disclosed, comprising thesteps of directing a plasma beam from a closed drift thruster at leastone area of an aligning substrate at an incident angle normal to thesubstrate to about 80° at a current density and ion energy for apredetermined amount of time to provide a substantially homeotropic modeof alignment for liquid crystals. In one embodiment, the current densityof the plasma beam is about 0.1 to about 1000 μA/cm² and the ion energyis from about 100 to about 2000 eV.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other features andadvantages will become apparent by reading the detailed description ofthe invention, taken together with the drawings, wherein:

FIGS. 1 a through 1 d show a schematic of the plasma source, profile ofthe discharge channel of the plasma source, and sample positions withrespect to plasma beam.

FIG. 2 shows plasma current versus gas (Ar) pressure curves for variousvalues of ion energy.

FIG. 3 a shows photos of combined cells having rubbed polyimidesubstrate as a reference substrate and plasma treated PVCN (polyvinylcinnimate) substrate as an object substrate. The object substrates wereirradiated in geometry 1 (FIG. 1 c). The plasma irradiation parameterswere α=60°, E=600 eV, τ_(exp)=2.5 min. The ion current density j isvaried; j=1, 2, 6, 8 and 25 μA/cm² in the cells 1, 2, 3, 5, and 5,respectively. The cells were 20 μm thick. They are filled with LC K15(4-cyano-4′-pentyl-1,1′-biphenylene). The cells were placed between pairof crossed polarizers. The pictures demonstrate alignment mode 1 incells 1 and 5, and alignment mode 2 in the middle part of cells 2-4corresponding to projection of the plasma beam.

FIG. 3 b presents the azimuth angle of the direction of LC alignment asa function of current density of Ar⁺ ions, starting from the directionof the incident plasma plane designated as 0° and rotate eitherclockwise or counterclockwise to 90° for the cells shown in FIG. 3 a.

FIG. 4 presents azimuth angles of the direction of LC alignment as afunction of irradiation time for the following plasma treated aligningsubstrates: PVCN, PI (polyimide), PMMA (polymethyl methacrylate)(square), PEMA (polyethyl methacrylate) (triangle). The substrates wereirradiated at the following conditions: α=60°, E=600 eV, j=8 μA/cm².

FIG. 5 presents photos taken between two crossed polarizers of twocombined cells having rubbed PI substrate as a reference substrate andplasma glass slide as an object substrate. The object substrates wereirradiated in geometry 1 (FIG. 1 c) through the mask opening of arectangular area in the middle of the substrate. The irradiationparameters for cell 1 and cell 2 were α=70°, E=400 eV, j=0.5 μA/cm²,τ_(exp)=2.5 min and α=70, j=6 μA/cm², E=500 eV, τ_(exp)=5 min,respectively. The cells were 20 μm thick. They are filled with LC K15.The cells are placed between a pair of crossed polarizers. The photosexhibit alignment mode 1 in cell (a) and alignment mode 2 in cell (b).The dark state of the oriented part of the cell (a) indicates that LCalignment on the plasma treated substrate is parallel to the alignmenton the reference substrate. Analogously, bright state of the cell (b)means that LC alignment on the plasma treated substrate is perpendicularto the alignment on the reference substrate. Both cells demonstrate highquality of LC alignment.

FIG. 6 shows symmetrical cells based on plasma treated PI substratesviewed through crossed polarizers. Treatment parameters α=60°, j=8μA/cm², E=600 eV, and τ_(exp)=2.5 min correspond to alignment mode 1.The substrates are combined to obtain parallel alignment (cell a) andtwist alignment (cell b). Cell gap was 20 μm.

FIG. 7 shows LC pretilt angle vs. plasma incidence angle α curves fordifferent substrates; ∘—PVCN, □—PI, ∇—PMMA, Δ—glass. The irradiationparameters for polymer and glass substrates were j=8 μA/cm², E=600 eV,τ_(exp)=2.5 min and j=0.5 μA/cm², E=400 eV, τ_(exp)=2.5 minrespectively. The cells gap was 20 μm.

FIG. 8 shows pretilt angle as a function of ion current density for PIsubstrate. The substrates were irradiated at the following conditions:α=60°, E=600 eV, τ_(exp)=2.5 min respectively.

FIG. 9 demonstrates light transmission versus applied voltage curves fortwist cells made of rubbed polyimide (□) and plasma beam treatedpolyimide (●) substrates. Plasma irradiation parameters: E=600V, J=8μA/cm², τ_(exp)=2.5 min, α=20°)^(t). Thickness of both cells was 6+/−0.2μm.

FIG. 10 shows combined LC cell viewed between a pair of crossed (a) andparallel (b) polarizers. The cell was made of rubbed PI substrate andplasma treated PVCN substrate. The latter substrate was two-stepirradiated with plasma beam in geometry 1 (FIG. 1 c); in the first stepthe substrate was entirely irradiated at α=70°, E=600V, j=8 μA/cm²,τ_(exp)=2.5 min (mode 1), then in the second step at α=70°, E=600V, j=8μA/cm², τ_(exp)=5 min (mode 2) through the mask. Two plasma treatmentsteps generate mutually perpendicular directions of LC alignment.

FIG. 11 a illustrates the first mode of alignment of the presentinvention wherein the easy axis of the liquid crystal molecules isoriented at an azimuth angle φ of 0° and the zenithal angle θ has avalue between 0° and about 40°.

FIG. 11 b illustrates the second mode of alignment wherein the easy axisof the LC molecules on the aligning substrate has an azimuth angle φequal 90°and a zenithal angle is 0°.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method of uniform (planar, tilted andhomeotropic) alignment of LCs. The method operates with collimated orpartially collimated plasma beams used to treat LC aligning substrates.

The materials that can function as aligning films in the presentinvention, which are cross-linked, degraded, etched, or otherwisemodified by the collimated or partially collimated plasma, can be oforganic or non-organic origin, or a combination thereof. The class oforganic aligning film materials includes, but is not limited to,photosensitive such as poly(vinyl cinnimate), or various unsaturatedpolyesters, and non-photosensitive polymers. Such polymers desirablyhave a high Tg such as at least about 100° C. and preferably at least150° C. Suitable examples of non-photosensitive polymer aligning filmmaterials include polyimide, various polyacrylates and methacrylatessuch as polymethyl methacrylate or polyethyl methacrylate, polyvinylacetate, and the like. The class of non-organic film materialscomprises, but is not limited to, glass, quartz, gold, indium tin oxide(ITO), silicon, silicon oxides (SiO₂, SiO_(x)), hydrogenateddiamond-like carbon (DLC), and hydrogenated amorphous silicon.

The films can be deposited on the substrate by any method as known tothe literature and to the art. Suitable examples of depositing theorganic films are spin coating and dip coating. For spin coating and dipcoating, proper solvent used should be capable of dissolving the organicmaterial. The methods suitable for depositing the non-organic filmsinclude, but are not limited to, vapor deposition (VD) in differentmodifications (physical VD, chemical VD, plasma enhanced chemical VD)ion beam sputtering, etc.

The substrate upon which the film is contained can be any materialcommonly used for fabricating liquid crystal cells. Materials such asglass, quartz or plastic such as polyether sulfone (PES), polycarbonate(PC), polyethylene terephthalate (PET), or triacetate cellulose (TAC)can be used. The substrate materials can also be any materials commonlyused for fabricating chips, for example silicon.

To treat the aligning film, any type of plasma source producingcollimated or partially collimated beam of plasma which has relativelylimited divergence can be employed such as those known to the art and tothe literature. In a preferred embodiment, the beam is characterized ashaving a full divergence angle of less than 30°. The gaseous feed usedto excite plasma include, but are not limited to, Ar, Kr, He, Xe, Ne,O₂, H₂, N₂, CH₄ and CF₄ and mixtures thereof, with the inert gases beingpreferable. Conventional collimated or partially collimated plasma beamscan be utilized to generate all types of uniform LC alignment describedabove. Closed drift thruster plasma generators are known to the art andto the literature and generally any type thereof can be used. The anodelayer thruster closed drift thruster utilized in the examples of theinvention was fabricated in the Department of Gaseous Electronics,Institute of Physics, Kyiv, Ukraine. Closed drift thrusters arecommercially available, for instance, from Izovac of Belarus and Veecoof the United States. As a plasma source, a closed drift thruster, whichis preferably an anode layer thruster specially designed to producecollimated or partially collimated plasma beams, can be used.

An example of a plasma source is illustrated in FIG. 1 in cross sectionand is an anode layer thruster. The plasma source 10 includes an outercathode 12 which serves as a north pole, an anode 14, and an innercathode 16 which serves as a south pole. In this embodiment asillustrated in FIG. 1 b, the discharge channel 18 located between innerand outer cathodes 16 and 12 respectively is generally in the shape ofan oval or race track. In a preferred embodiment, the straight portionsof the channel are utilized to irradiate aligning substrates and are inthe shape of sheet-like fluxes. The sheet like plasma fluxes produced bythe anode layer sources easily treats large-area substrates (usingtranslation method). The plasma flux 20 emanates from discharge channel18 onto a designated portion of aligning substrate or sample 22 situatedon substrate holder 24 which can be stationary or a conveyor in order toconvey one or more substrates into and out of the plasma flux beam path.That is, in one embodiment, a conveyor can be utilized, moving at apredetermined rate, to convey a series of aligning substrates throughthe beam path formed by the plasma source, at a predetermined time ofexposure whereby a number of aligning substrates can be treated in aconsistent economical fashion. Vacuum chamber 30 also includes window 38and gas valves 32, 34, and 36 which can be inlets, outlets, pumps, orcombinations thereof.

The plasma source preferably is operating utilizing direct current andcapable of producing a flux of plasma that is extracted and acceleratedelectrostatically.

The anode layer thruster generally belongs to the family of closed driftthrusters, see V. Zhurin, H. Kaufman, and R. Robinson, “Physics ofclosed drift thrusters”, Plasma Sources Sci. Technol., 8, R1-R20 (1999).Closed drift thrusters do not have filaments or secondary electronsources to initiate discharge current or to neutralize the beam. Sincethe ions are accelerated electrodynamically, grids to extract andaccelerate ions are not needed and are thus not present as in typicalion beam sources. The plasma source has permanent magnets at the innerand outer cathodes with the anode mounted in the space therebetween.Together the electrodes define the size and shape of the dischargechannel. The ion flux is formed in crossed electric (E) and magnetic (H)fields within the discharge channel and is a part of direct currentplasma generated therein.

The plasma beam from a closed drift thruster, unlike an ionic beam suchas from a Kaufman ion beam source contains a number of components: ions,neutral atoms, electrons, protons, and deep UV (wavelength about lessthan 250 nanometers). This feature expands the aligning abilities of thetechnique, as not only the ions can be involved in the formation of thealigned substrates but other components too which believably modify theLC alignment. For example, the deep UV irradiation accompanying theplasma beam can be used for additional photoalignment of the treatedsubstrate. Third, the processing with the isotropic plasma previouslyutilized to modify zenithal alignment by the plasma-chemical treatmentof the aligning substrates (grafting, polymerization, oxidation) can bereplaced by the processing with collimated or partially collimatedplasma beams to control both zenithal and azimuthal alignment.

The plasma alignment technique of the present invention yields at leasttwo different modes of alignment, with the resulting easy axis beingeither parallel as in the first mode or perpendicular as in the secondmode to the incident plane, in contrast to the ionic beam techniques,which produce only one direction. It is also believed that additionalmodes can be achieved, with the zenithal angle θ between 0° and lessthan about 40° and the azimuth angle φ between 0° and 90°, between thefirst and second modes.

Homeotropic LC alignment can be generated by both oblique and normalincidence of the incidence of plasma flux. In the former case, by thechange of irradiation parameters (ion density and energy, irradiationtime), two various alignment modes can be obtained. First of all, thesemodes differ by orientation of the induced easy axes (i.e., thedirection of preferable orientation of the long axis of LCmolecules): 1) a first easy axis is confined to the incident planeformed by the direction of the beam and the normal to the treatedsubstrate; 2) a second easy axis is in the plane of film (perpendicularto the plane of incidence). By increasing the irradiation dose one canchange the alignment direction from the type 1 to the type 2. For thealignment mode 1 (oblique incident of plasma flux), the value of thepretilt angle can be controlled with irradiation parameters (irradiationangle, ion current density, ion energy, etc.). The alignment mode 2 ischaracterized by a zero pretilt. The first and second alignment modescan be briefly described with the angles φ and θ introduced above thecharacterized uniform LC alignment. Assuming that azimuth angle φ is therotational angle between projections of plasma beam and easy axis (longaxis) of LC molecules on the substrate, one can summarize that, in caseof the mode 1, φ=0°, θ≧0° in particular 0° or 0.1° to about 10° or about40°, whereas, in case of the mode 2, φ=preferably about 90° or generally70° to 110°, and θ=about 0°.

The liquid crystal alignment methods of the present invention canutilize various combinations of irradiation parameters in order toobtain any of the various alignment modes. The ion current density, j,utilized in the present invention ranges generally from about 0.1 toabout 1000, and preferably from about 0.5 to about 30 μA/cm². The ionenergy, E, is utilized in a range generally from about 50 to about5,000, desirably from about 150 to about 1000, and preferably from about200 or about 250 to about 400 or about 600 eV. The ion energy rangescorrespond to using Ar source gas and can change when other gasses areutilized. The time of exposure to irradiation generally depends on thecurrent density and varies generally from about 5 seconds to about 30minutes, and preferably from about 10 seconds to about 10 minutes. Thepressure p in the plasma source chamber can vary in a broad range, fromabout 1.0×10⁻⁵ to about 1.0×10⁻², desirably from about 1.0×10⁻⁴ to about1.0×10⁻³, preferably from about 2.0×10⁻⁴ to about 10.0×10⁻⁴ Torr. Theplasma beam from the plasma source can be oriented with respect to thesubstrate surface at an angle α generally greater than 0°, the positionnormal to the substrate, to about 85°, desirably from about 10°to about80° and preferably from about 45 to about 65°. A greater pretilt angleis achieved at around 45°, i.e., between about 30° and about 60°.

The two mode alignment feature is typical for organic and non-organicaligning layers, and it is observed for various kinds of LCs, boththermotropic and lyotropic types. That is, generally any type of liquidcrystals can be utilized in the method of the present invention, withliquid crystalline phases comprising nematic, smectic, and cholestericliquid crystals, preferably nematic crystals. The feature of two-modealignment can be used to generate alignment with desirable parameters aswell as to prepare LC cells having predetermined patterns. In oneembodiment, alignment patterns can be created using masks such as paperor plastic, placed onto the target substrate which do not allow passageof the plasma beam therethrough. Masking techniques are well known tothose of ordinary skill in the art.

It is an important fact that LC alignment preliminarily induced byplasma beam can be modified, or even overwritten, by subsequent plasmairradiation steps. This feature, for instance, can be used to generatepretilt angle on the substrates preliminarily treated to align LCs inmode 2. Also, the possibility to overwrite alignment reduces a number ofmasking processes used for cell patterning. Particularly, for two-domainalignment only one mask is required.

The plasma treatment of the present invention can override alignmentinduced with other methods (e.g., rubbing, photoalignment, etc.). Thismeans that plasma method may be successively combined with other methodsfor sample patterning.

The plasma treated alignment layer can be placed on one or both of thesubstrates in conventional liquid crystal cells. When the plasma treatedlayer is placed on only one of the substrates, any known alignmentmaterial may be placed on the remaining substrate. Other alignmentmaterials include, but are not limited to, rubbed or light-irradiatedpolyimides, light-irradiated polyvinyl cinnimate, oblique depositedSiO_(x).

The LC alignment on plasma treated substrates is extremely photo andthermally stable. The photo and thermal stability are comparable withthose for rubbing method.

The invention will be better understood by reference to the followingdescription and examples which to serve to illustrate, but not to thelimit the scope of the present invention.

The films of photosensitive and non-photosensitive polymers were used asorganic aligning films. The films were obtained by spin coating polymersolution onto substrates such as bare glass or indium tin oxide (ITO)coated glass slides.

To treat the substrates, the following set up was utilized wherein ananode layer plasma source such as an electrodynamic thruster was usedwhich is known to the art and to the literature. The source wasspecially designed to produce a collimated or partially collimated fluxof plasma from the argon which was used as the gaseous feed describedherein. The sketch of the anode layer thruster is shown in FIG. 1 a.

The anode layer thruster with the race track shape of the dischargechannel (see FIG. 1 b) was mounted in vacuum chamber 30 (see FIG. 1 a).The channel 18 had an elongated shape to produce sheet-like plasmabeams. The chamber was pumped out up to pressure 10⁻⁵ Torr, and then isfilled by argon. The working pressure p in our experiments was between2.0×10⁻⁴ and 10.0×10⁻⁴ Torr. The pressure of Ar determines currentdensity j of the plasma ions Ar⁺. The j versus p curves for variousvalues of the anode potential U are presented in FIG. 2. The anodepotential also determines ion energy E. The E was varied within 200-900eV.

Substrate holders 24 were mounted in vacuum chamber 30 just underdischarge channel 4 (FIG. 1 a). The distance between plasma outlet andirradiated substrate was about 10 cm. The distance between the substrateand plasma outlet can be varied between about 5 and about 50 cm, andpreferably is about 5 to about 20 cm. The holder could be rotated toperform irradiation in geometry 1 (FIG. 1 c), when the substrate wastilted in the direction perpendicular to plasma sheet; and geometry 2(FIG. 1 d), when the substrate was tilted in plane of the plasma sheet.The plasma beam incidence angle α could be varied within 0° and 85°.

For evaluation of alignment of thermotropic liquid crystals, twodifferent kinds of LC cells were prepared: In cells of the first typeone substrate was irradiated by plasma beam, while the second one was arubbed polyimide layer (combined or asymmetrical cells). In cells of thesecond type both substrates were irradiated by plasma beam (symmetricalcells). To get an antiparallel director configuration, the irradiationdirections of the two substrates were antiparallel. The cell gap wasmaintained with spacers of 6 μm and 20 μm in diameter. The cells werefilled with nematic LC materials of positive dielectric anisotropy Δ∈>0,such as K15 pentylcyanobiphenyl (5CB) and ZLI 4801-000 available fromMerck, or nematic LC MLC6610 with a negative dielectric anisotropy Δ∈≦0,from Merck. The symmetrical cells were used to determine pretilt angleof LC by crystal rotation technique. Using combined cells, direction ofLC azimuthal alignment was determined. In addition, these cells wereused to estimate azimuthal anchoring energy connected with the twistangle of LC experimentally measured. To evaluate the alignment oflyotropic liquid crystals, we used cells comprised of pairs of bareglass substrates (microscope slides from Fisher Scientific). Onesubstrate was irradiated by the plasma beam, whereas the second was nontreated. The direction of alignment in these cells was determined byobservation of interference colors under polarizing microscope withquartz plate.

The examples presented below illustrate abilities of the suggestedtechnique and properties of the obtained alignment of LCs. The examplesare divided into 3 groups; the first group (examples 1.1-1.17)demonstrates possibilities to generate various alignment modes, thesecond group (examples 2.1-2.17) is focused on control of alignmentparameters (pretilt angle, anchoring energy, etc.), and the third one(example 3.1-3.3) considers the method of cell patterning.

Example 1.1

The polyvinyl cinnimate photosensitive polymer film from Aldrich wasdissolved in dichloroethane (weight concentration of 20 g/l). A dropletof this solution was deposited on a rectangular glass substrate (2×3 cm)containing ITO electrode and spin-coated for 30 seconds at 2500 rpm.Then the substrate was maintained for 2 hours at 90° C. to remove thesolvent. As a result, a uniform polymer film, was produced.

The substrate coated with PVCN (Polyvinyl cinnimate) film was subjectedto plasma irradiation in geometry 1 (FIG. 1 c). The irradiationparameters were as follows: plasma incidence angle α=70°, ion currentdensity j=1 μA/cm², ion energy E=600 eV, irradiation time τ_(exp)=5 min.

The combined cells were prepared in which aligning layers were,respectively, plasma treated layer (object substrate) and rubbedpolyimide layer (reference substrate). The rubbing directioncorresponded to a long side of the rectangular substrate. The cell witha gap of 20 μm was prepared and filled with LC K15 of positivedielectric anisotropy Δ∈>0. The picture of this sample viewed betweencrossed polarizers is presented in FIG. 3 a (picture 1). The dark colorof the cell shows that azimuthal alignment direction on the objectsubstrate is parallel to the rubbing direction on the referencesubstrate. This implies that the alignment direction on the plasmatreated substrate is confined to the incidence plane of plasma beam.This type of alignment has been defined as alignment mode 1.

Example 1.2

A combined cell is prepared as in Example 1.1 except the cells arefilled with LC ZLI 4801-000 of positive dielectric anisotropy Δ∈>0. Theobtained alignment of LC corresponds to alignment mode 1.

Example 1.25

A combined cell is prepared as in Example 1.1 except the cells werefilled with LC MLC6610 of negative dielectric anisotropy Δ∈<0. Theobtained alignment of LC corresponded to alignment mode 1.

Example 1.3

A series of combined cells (5 cells) is prepared. The cell preparationprocess is as in Example 1 except the value of current density j ofplasma ions was varied (j=1, 2, 6, 8, 12, 25 μA/cm²). The pictures ofthe obtained samples are presented in FIG. 3 a (pictures 1, 2, 3, 4, and5, correspondingly). The white area in the cells 2-4 corresponds tocentral part of the plasma beam, whereas the black areas corresponded tothe peripheral part of the beam. The alignment in the black areacorresponds to alignment mode 1, while the alignment in the white areacorresponds to the new type of alignment. The LC easy axis in the whitearea is oriented perpendicularly to rubbing direction on the referencesubstrate. This means that the easy axis is induced perpendicularly tothe plane of the plasma beam incidence. This type of alignment has beendefined as alignment mode 2. The azimuth angle of the easy axis on theplasma treated substrate φ (the angle between projection of plasma beamand LC easy axis on the plane of substrate) as a function of j ispresented in FIG. 3 b. The threshold-like transition from the mode 1 tothe mode 2 is realized in the relatively narrow range of the currentdensity of plasma ions (2 μA/cm²<j<12 μA/cm²).

Example 1.4

A series of combined cells was prepared as in Example 1.1 except theobject substrates were treated with plasma beam in geometry 2 (see FIG.1 c). The LC alignment results were same as in Example 1.3

Example 1.5

A series of combined cells (8 cells) were prepared. The cell preparationprocess is as in Example 1.1 except that irradiation time was varied(τ_(exp)=2.0, 3.0, 3.5, 4.5, 5, 6.5, 10, 15 min) and the ion currentdensity was fixed (j=8 μA/cm²). The azimuth angle φ of the LC easy axisas a function of τ_(exp) is presented in FIG. 4. As one can see, thethreshold-like transition from the alignment mode 1 to the alignmentmode 2 is observed in the range 4 min<τ_(exp)<5 min at the indicatedcurrent density.

Example 1.6

A series of combined cells was prepared in Example 1.5 except the objectsubstrates are treated with plasma beam in geometry 2 (see FIG. 1 c).The φ vs. τ_(exp) curve was same as in example 1.5.

Example 1.7

A series of combined cells was prepared as in Example 1.5 except theobject substrates contain polyimide (PI) aligning films. The films wereprepared as follow. The 15 g/l solution of polyimide 2555 by Dupont wasspin coated on the glass slides (2,500 rmp, 30 min). In the followingthe substrates were baked for 10 min at 90° C. and, subsequently, 2 h at200° C. The φ vs. τ_(exp) curve was same as in Example 1.5, see FIG. 4.

Example 1.8

A series of combined cells was prepared as in Example 1.5, except theobject substrates contained polymethylmethacrylate (PMMA) aligningfilms. The films were prepared as follow. The 10 g/l solution of PMMA byAldrich was spin coated on the glass slides. The substrates were baked 2h at 150° C. The dependence of the azimuth angle of the LC easy axis onthe exposure time τ_(exp) is the same as in Example 1.5, see FIG. 4.

Example 1.9

A series of combined cells was prepared as in Example 1.5 except theobjection substrates contain polyethylmethacrylate (PEMA) aligningfilms. The films were prepared as follows. The 10 g/l solution of PS byAldrich was spin coated on the glass slides. In the following thesubstrates were baked 2 h at 150° C. Same as in Example 1.5 thetransition from alignment mode 1 to alignment mode 2 is observed withthe increase of τ_(exp). However, compared with PVCN, PI, and PMMA, thetransition is realized at higher values of τ_(exp).

Example 1.10

A PVCN aligning film on a glass slide was prepared as in Example 1.1.The film was treated with plasma beam at the parameters corresponding toaligning mode 1: α=60°, j=8 μA/cm², E=600 eV, τ_(exp)=2.5 min.

The cell is prepared as in Example 1.1, except that the substrates arecombined so that 90° twist LC alignment was obtained (irradiationdirection of the object substrate was perpendicular to rubbing directionof the reference substrate). The azimuth anchoring energy on the plasmatreated substrate was estimated to be about 10⁻³ erg/cm².

Example 1.11

A PVCN aligning coating on a glass slide was prepared as in Example 1.1.The film was treated with plasma beam at the parameters corresponding toaligning mode 2: α=60°, j=8 μA/cm², E=600 eV, τ_(exp)=2.5 min.

The cell was prepared as in Example 1.1, except that the substrates werecombined so that 90° twist LC alignment was obtained (irradiationdirection of the object substrate was perpendicular to rubbing directionof the reference substrate). The azimuth anchoring energy on the plasmatreated substrate was estimated to be about 10⁻³ erg/cm².

Example 1.12

A bare glass substrate (microscope slide from Fisher Scientific) wasirradiated in a geometry 1 (FIG. 1 c) at the following conditions:α=70°, j=0.5 μA/cm², E=400 eV, τ_(exp)=2.5 min. The substrate wasirradiated through a mask of aluminum foil, wherein only the centralpart of the substrate was exposed.

The combined cell was prepared as in Example 1.1. The picture of thissample in crossed polarizers is presented in FIG. 5 a. As can be seen,alignment mode 1 is realized in the irradiated area (black square in themiddle of the cell).

Example 1.13

The bare glass substrate (microscope slide from Fisher Scientific) wasirradiated in a geometry 1 (FIG. 1 c) at the following conditions:α=70°, j=6 μA/cm², E=500 eV, τ_(exp)=5 min. The substrate was irradiatedthrough the mask from aluminum foil, which opens only central part ofthe substrate.

The combined cell was prepared as is described in Example 1.1. Thepicture of this sample in crossed polarizes was presented in FIG. 5 b.The alignment mode 2 was realized in the plasma irradiated area (whitesquare in the middle of the cell).

Example 1.14

A combined cell was prepared as in Example 1.12, except that the objectsubstrate was an ITO covered glass slide. Same as in Example 1.12,alignment mode 1 was realized.

Example 1.15

A combined cell was prepared as in Example 1.13, except that the objectsubstrate was an ITO covered glass slide. Same as in Example 1.12,alignment mode 2 was realized.

Example 1.16

A combined cell was prepared as in Example 1.12, except that the objectsubstrate was a bare quartz slide and the cell is filled with LC ZLI4801-000. The alignment mode 1, same as in Example 1.11, was realized.

Example 1.17

A combined cell was prepared as in Example 1.13, except that the objectsubstrate was a bare quartz slide and the cell was filled with LC ZLI4801-000. The alignment mode 2, same as in Example 1.12, was realized.

Example 2.1

Two films of polyimide 2555 (Dupont) on glass substrates were preparedas in Example 1.7. These films were subjected to plasma irradiation ingeometry 1 (FIG. 1 c). The irradiation parameters were: α=60°, j=8μA/cm², E=600 eV, τ_(exp)=2.5 min. Following Example 1.7, theseparameters corresponded to generation of alignment mode 1.

The substrates are used to prepare symmetrical cell. To get anantiparallel director configuration in the cell, the irradiationdirections were antiparallel. The cell gap was 20 μm. The cell wasfilled with LC K15. The picture of this cell in crossed polarizers ispresented in FIG. 6 (photo a). LC director was tilted towards directionof irradiation. The value of pretilt angle of the LC was determined tobe 5.5°.

Example 2.2

A symmetric cell was prepared as in Example 2.1 except that substratesare irradiated in geometry 2 (FIG. 1 c). Same as in Example 2.1, LCdirector was tilted towards direction of irradiation. The value of LCpretilt angle was about 5°.

Example 2.25

A symmetric cell was prepared as in Example 2.1 and filled with LCMLC6610 with negative dielectric anisotropy Δ∈<0. LC director was tiltedtowards direction of irradiation. The value of pretilt angle of the LCwas determined to be 28°.

Example 2.3

Polyimide coated substrates were prepared and treated as in Example 2.1.A symmetrical cell with twisted director configuration was prepared. Forthis purpose the substrates were combined so that irradiation directionswere perpendicular. The picture of this cell in crossed polarizers ispresented in FIG. 6 (photo b).

Example 2.4

A series of symmetric cells was prepared as in Example 2.1, except thatincidence angle was varied; α=0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°,80°. The uniform alignment was achieved for α=20°-80°. The θ versus αcurve is shown in FIG. 7.

Example 2.5

A series of symmetric cells was prepared as in Example 2.4 except thataligning substrates were covered by PVCN films prepared as in Example1.1. The uniform alignment was achieved for α=20°-80°. The θ versus αcurve is shown in FIG. 7.

Example 2.6

A series of symmetric cells was prepared as in Example 2.4 except thataligning substrates were covered by PMMA films prepared as in Example1.8. The uniform alignment was achieved for α=20°-80°. The versus acurve is shown in FIG. 7.

Example 2.7

A series of symmetric cells was prepared as in Example 2.4 except thataligning substrates were bare glass substrates (Fisher Scientific)treated as in Example 1.11, except that incidence angle was varied;α=0°, 10°, 20°, 40°, 50°, 60°, 70°, 80°. The uniform alignment wasachieved for α=30°-80°. The θ versus α curve is shown in FIG. 7.

Example 2.8

Bare glass substrates (Fisher Scientific) were treated with plasma atthe following conditions: α=60°, j=8 μA/cm², E=600 eV, τ_(exp)=5 min. Asymmetric cell is assembled as in Example 2.1. The cell was filled withLC K15. Homeotropic LC alignment in the cell was observed.

Example 2.9

The sample was prepared as in Example 2.8, except substrates wereirradiated at normal incidence of plasma beam. Homeotropic LC alignmentin the cell was observed.

Example 2.10

The sample was prepared as in Example 2.9, except the substrates werebare slides of quartz. Homeotropic LC alignment in the cell wasobserved.

Example 2.11

A series of symmetric cells was prepared as in Example 2.1, except thation current density j was varied; j=2.5, 8, 20, and 35 μA/cm². The θversus j curve is shown in FIG. 8.

Example 2.12

PVCN substrates were prepared as in Example 1.1 and treated with plasmain geometry 1 at the parameters: α=60°, j=8 μA/cm², E=600 eV, τ_(exp)=5min. Following Example 1.5, the irradiation conditions correspond to thealignment mode 2. The substrates were combined so that directions ofplasma irradiation were antiparallel. The thickness of the cell was 20μm. The cell was filled with LC K15. The tilt angle of LC in the cellwas about 0°.

Example 2.13

A symmetric cell was prepared as in Example 2.11, except that substratesare combined so that directions of plasma irradiation were parallel. Thetilt angle of LC K15 in the cell was about 0°.

Examples 2.12 and 2.13 show that pretilt angle of LC K15 on PVCNsubstrates in case of alignment mode 2 is 0°.

Example 2.14

Two symmetric cells were prepared as in Example 2.12 and Example 2.13,respectively. The cells were filled with LC ZLI 4801-000. The crystalrotation studies show that pretilt angle of LC is about 0°.

Example 2.15

Two symmetric cells were obtained as in Example 2.12 and Example 2.13,respectively, except the substrate were irradiated in geometry 2. Thecrystal rotation studies show that pretilt angle of LC is about 0°.

Example 2.16

Two polyimide substrates were prepared as in Example 1.7. The films wereirradiated at α=60°, j=8 μA/cm², E=600 eV, τ_(exp)=10 min and,subsequently, at α=60°, j=8 μA/cm², E=600 eV, τ_(exp)=2 min. After thefirst irradiation step the substrates were rotated so that the seconddirection of plasma irradiation were perpendicular to the first one.Using these substrates symmetric cell was prepared. The substrates werecombined as a cell so that directions of the second plasma irradiationwere antiparallel. The thickness of the cell was 20 μm. The cell wasfilled with LC K15. Tilted alignment of LC is observed. LC director wastilted towards direction of second irradiation. The value of pretiltangle was about 3.5°.

Example 2.17

Two polyimide films were prepared as in Example 1.7. The films wereirradiated at the following conditions; (1): α=60°, j=8 μA/cm², E=600eV, τ_(exp)=2 min, and (2) α=60°, j=8 μA/cm², E=600 eV, τ_(exp)=10 min.Using these substrates symmetric cell was prepared. By cell assembling,the substrates were combined so that directions of plasma beam incidencewere antiparallel. The thickness of the cell was 20 μm. The cell wasfilled with LC K15. Twist alignment of LC in the cell (twist angle about90°) was observed.

Example 2.18

Two polyimide substrates were prepared as in Example 1.7. The films wereirradiated at the following conditions: α=60, j=8 μA/cm², E=600 eV,τ_(exp)=10 min. Using these substrates symmetric cell was prepared. Bycell assembling the substrates were combined so that incidencedirections of plasma beam were mutually perpendicular. The thickness ofthe cell was 6 μm. The cell was filled with LC K15. Twist alignment ofLC in the cell (twist angle about 90°) was observed. The cell was placedbetween parallel polarizers and subjected to alternative electric field(sine-like signal, f=1 kHz). The transmittance versus voltage curve waspresented in FIG. 9 (curve 1).

Curve 2 in FIG. 9 corresponds to another cell. The cell was prepared asprevious one except polyimide films are subjected to rubbing instead ofplasma irradiation. Curves 1 and 2 are very similar. Thus, the cellsbased on plasma alignment and rubbing alignment show identicalelectroptic performance.

Practically all methods of the cell patterning known for photoalignmentand ion beam alignment technique can be applied for the plasma beamalignment. We consider below only several additional methods based onpossibility to induce various alignment modes.

Example 3.1

Polyvinyl cinnimate film on the glass substrate (3×2 cm) was prepared asin Example 1.1. The film was irradiated in geometry 1 at the followingparameters: α=70°, j=8 μA/cm², E=600 eV, τ_(exp)=2 min. The irradiationconditions correspond to induction of the alignment mode 1. Then thefilm was covered with aluminum mask and irradiated again without changeof the sample position. The irradiation parameters of the secondirradiation are α=70°, j=8 μA/cm², E=600 eV, τ_(exp)=10 min. Theycorrespond to alignment mode 2.

The combined cell was prepared from the said plasma treated substrateand rubbed PI substrate. Rubbing direction of the rubbed substrate wasantiparallel to the plasma irradiation direction of the plasma treatedsubstrate. The cell gap was 20 μm. The cell was filled with LC K15. Thepicture of this cell was shown in FIG. 10. One can see alignment domainswith mutually perpendicular directions of easy axis in the azimuthplane.

Example 3.2

The cell was prepared as in Example 3.1 except the first plasmatreatment is replaced by irradiation with UV light from mercury lamp.The light polarized by Glan polarizing prism is directed normally to thesubstrate. The light polarization corresponds to the long side of thesubstrate. The light intensity and irradiation time was 12 mW/cm² and 15min, respectively. Same as in Example 3.1, the alignment domains withmutually perpendicular directions of easy axis in the azimuth plane areobserved.

Example 4.1

To demonstrate the plasma alignment of a lyotropic LC in the alignmentmode 1, we used a 14 weight % water solution of the lyotropic chromonicLC (LCLC) material disodium cromoglycate (DSCG) also known as cromolyn(C₂₃H₁₄O₁₁Na₂). The cells were made by using two bare glass substrates,cut from microscope slides from Fisher Scientific. One substrate wasirradiated in a geometry 1 (FIG. 1 c) at the following conditions:α=70°, j=0.5 μA/cm2, E=400 eV, τ_(exp)=2.5 min, as in Example 1.12. Thesecond substrate was not treated. The cell thickness was controlled by20 micron mylar spacers. The LCLC demonstrated alignment mode 1 with thedirector in the incident plane with the pretilt angle close to zero. Thealignment direction was determined from the birefringence colorsobserved under the polarizing microscope with quartz plate. Placement ofthe LCLC material between two untreated bare glass substrates produced amisaligned sample.

Example 4.2

To demonstrate the plasma alignment of lyotropic LC in the mode 2, weused the same LCLC material as in Example 4.1, in the cells made of twobare glass substrates, cut from microscope slides from FisherScientific. One substrate was irradiated in a geometry 1 (FIG. 1 c) atthe following conditions: α=70°, j=6 μA/cm², E=500 eV, τ_(exp)=5 min, asin Example 1.13. The second substrate was not treated. The cellthickness was controlled by 20 micron mylar spacers. The LCLCdemonstrated alignment mode 2 with the director perpendicular to theincident plane with a zero pretilt angle. The alignment direction wasdetermined from the birefringence colors observed under the polarizingmicroscope with quartz plate. Placement of the LCLC material between twountreated bare glass substrates produced a misaligned sample.

The liquid crystals utilized are conventional and known to the art.Desirably they are nematic liquid crystals which are generallycharacterized by a rod-like appearance of a single component orcommercially available eutectic mixture. Alternatively, ferroelectricliquid crystals can be utilized such as those optically-active singlecomponents, exhibiting a smectic C phase with tilted layer structure.

In accordance with the patent statutes, the best mode and preferredembodiment have been set forth, the scope of the invention is notlimited thereto, but rather by the scope of the attached claims.

1. A method for generating an alignment direction on an aligningsubstrate for liquid crystal cells, comprising the steps of: directing aplasma beam from a closed drift thruster at least one area of analigning substrate at an incident angle of greater than 0°, wherein 0°is normal to the substrate, to about 85° at a current density and ionenergy for a predetermined amount of time to induce a surface anisotropyand an alignment direction on the area of the aligning substratebombarded by the plasma beam and provide a mode of alignment for liquidcrystals, wherein an azimuth angle has a reference axis that is aprojection of the plasma beam on the aligning substrate in the firstbombarding step and a zenithal angle is an angle between the alignmentdirection and the alignment substrate, wherein i) the plasma beambombarded portion of the aligning substrate imparts to a liquid crystalthe alignment direction having an azimuth angle φ of 70° to 110° and azenithal angle θ of about 0°; or ii) the plasma beam bombardmentincludes a second bombarding step and after the first bombarding step,wherein the substrate or plasma source is rotated so that in the secondbombarding step, the direction of plasma irradiation is perpendicular tothe irradiation of the first bombarding step, wherein the bombardedportion of the alignment substrate imparts to a liquid crystal thealignment direction having an azimuth angle φ of 90° and a zenithalangle θ of 0° to 5°.
 2. The method according to claim 1, wherein thealigning substrate comprises an organic or inorganic aligningcomposition.
 3. The method according to claim 2, wherein the currentdensity of the plasma beam is about 0.1 to about 1000 μA/cm², andwherein the ion energy is from about 100 to about 2000 eV.
 4. The methodaccording to claim 3, wherein said closed drift thruster is an anodelayer thruster.
 5. The method according to claim 3, wherein the aligningsubstrate comprises an aligning film, wherein the aligning filmcomprises polyvinyl cinnamate, unsaturated polyester, a polyimide,poly(meth)acrylate, polyvinyl acetate, glass, quartz, gold, indium tinoxide, silicon, silicon oxide, hydrogenated diamond-like carbon, orhydrogenated amorphous silicon.
 6. The method according to claim 5,wherein in the i) alignment direction the azimuth angle φ is about 90°.7. The method according to claim 6, wherein the current density of theplasma beam is about 0.5 to about 30 μA/cm², and wherein the ion energyis from about 200 to about 700 eV.
 8. The method according to claim 3,wherein the incident angle is about 20° to about 85°.
 9. The methodaccording to claim 7, wherein the incident angle is about 50° to about75°.
 10. The method according to claim 1, further including a step offorming a liquid crystal cell comprising the i) or the ii) aligningsubstrate and thermotropic or lyotropic liquid crystals.
 11. The methodaccording to claim 4, further including a step of forming a liquidcrystal cell comprising the i) or the ii) aligning substrate andthermotropic or lyotropic liquid crystals.
 12. The method according toclaim 1, further including a step of utilizing a mask to prevent theplasma beam from reaching a predetermined portion of the aligningsubstrate.
 13. The method according to claim 4, further including a stepof utilizing a mask to prevent the plasma beam from reaching apredetermined portion of the aligning substrate.
 14. The methodaccording to claim 1, wherein the plasma beam is in the form of a sheet.15. The method according to claim 4, wherein the plasma beam is in theform of a sheet.
 16. The method according to claim 1, further includingthe step of moving the aligning substrate through a path of the plasmabeam.
 17. The method according to claim 4, further including the step ofmoving the aligning substrate through a path of the plasma beam.
 18. Themethod according to claim 7, further including the step of moving thealigning substrate through a path of the plasma beam.
 19. The methodaccording to claim 1, wherein the aligning substrate is positioned at adistance of about 5 to about 50 cm from a source of the plasma beam. 20.The method according to claim 4, wherein the aligning substrate ispositioned at a distance of about 5 to about 50 cm from a source of theplasma beam.
 21. The method according to claim 7, wherein the aligningsubstrate is positioned at a distance of about 5 to about 50 cm from asource of the plasma beam.
 22. The method according to claim 1, whereinthe plasma beam bombarding provides the alignment direction i), andwherein the liquid crystals are thermotropic or lyotropic liquidcrystals.
 23. The method according to claim 1, wherein the plasma beambombarding provides the alignment direction ii), and wherein the liquidcrystals are thermotropic or lyotropic liquid crystals.